1. Field of the Invention
This invention pertains to a fuel-injection device which controls the amount of fuel-injection in an internal combustion engine by an opening/closing control of a solenoid valve installed at some point along a fuel-supply passage leading to the compressor of a fuel injection pump.
2. Related Art
Regarding fuel-injection devices, for example, the device disclosed in Japanese Kokai Patent Publication No. 61-268844 is well-known.
With this device, as shown by the formula (1) below, a pulse width Td for operating the solenoid valve is determined by the sum of the time delay in opening/closing of the valve and the injection time Tq corresponding to the desired injection level, to control the fuel-injection level of the internal combustion engine. EQU Td=Tv+Tq formula (1)
The Tv is almost constant regardless of the injecting conditions, and the drive pulse width Td can be adjusted by changing the Tq. FIG. 5 shows an ordinary injection-level control.
Once the drive pulse (Dp) corresponding to the Td is generated, based on this Dp, the solenoid valve is supplied with current which is generated for the time length Tv necessary to completely close the solenoid with greater valve lift, and with the current that is put out during the time length Tq necessary to keep the valve closed (the condition when DVC is high).
In the aforementioned control, to obtain a minimal injection level, the Tq can be set at 0, and Td=Tv, as shown by the broken lines in FIG. 6. However, when the solenoid valve is actually controlled by the Tv pulse width, electrical conduction to the solenoid valve is continued until the communication between the high-pressure side and the low-pressure side is cut off; therefore, some time passes before the solenoid valve is completely opened again as it was in the earlier driving condition, and a substantial amount of fuel is injected due to the preflow caused by an injection pressure rise that occurs at this time.
This fuel-injection becomes significant as the rotation rate increases and the oil supply rate from the pumping system becomes greater; therefore, the inconvenience is that injection control is impossible when the engine load is small and the engine rotation rate is great (high idle time), in other words, when the domain below the a line in FIG. 7 is larger.